1. Technical Field
The present invention relates to a method of removing calcium from a hydrocarbon fraction, and more particularly to a method of removing calcium from a hydrocarbon fraction using an extraction agent including 2-oxopropanal or derivatives thereof.
2. Description of the Related Art
Generally, most onshore and offshore oil fields include heavy oil containing metal impurities such as calcium. In particular, among offshore oil fields containing large amounts of organic acids, during the production process, the organic acid contained in oil is coupled with a salt, especially calcium, contained in water supplied for oil production, thereby generating organic calcium. In some cases, such calcium is melted in oil, resulting in high calcium content in oil.
Such high-calcium oil has been excluded from development because of low economic benefits in the past, but the fact that high economic margin or sale margin are being ensured by virtue of processing of impurities is known these days, and many countries and companies have become interested in the development of related oil fields, and are actually involved in such development. Typical high-calcium oil fields include Doba and Kuito in West Africa and Heidrum and Captain in the North Sea, as well as Bohai Bay and Shengli in China and Serang in Indonesia, Asia. As shown by these examples, these high-calcium oil fields are distributed all over the world.
With regard to typical crude oil, calcium is mainly present in the form of a salt such as CaCl2, and is easily removed through a desalting process. However, in the case of oil from oil fields, calcium is mostly present in the form of calcium naphthenate in which calcium is coupled with an organic acid such as naphthenic acid. Calcium naphthenate (CaNA) is configured such that the anion of naphthenic acid is coupled with the calcium cation, and also is characterized in that the chemical structure of the anion of naphthenic acid varies widely. Such calcium naphthenate, which is both hydrophilic and hydrophobic, is almost impossible to treat because it improves the stability of an emulsion produced during the desalting process.
Meanwhile, calcium in crude oil entails the following problems in the individual steps of the refinery process.
1) Oil tank farm—high BS&W (Basic sediment and water)
2) Desalting—emulsion level control, a decrease in voltage due to high conductivity of calcium (Ca)
3) Wastewater treatment—water carryover, poor effluent water quality
4) Heat exchanger and preheater—calcium deposits and low heat exchange efficiency
5) FCCU (Fluid Catalytic Cracking Unit) or RFCCU (Residue Fluid Catalytic Cracking Unit)—catalyst inactivation
6) High calcium content in coke and heavy fuel oil
Because of these problems, high-calcium crude oil having high calcium content trades at lower prices than typical light oil. In the refinery industry, such high-calcium crude oil is being processed in a manner in which it is partially diluted with high-quality light oil.
These days, research is ongoing into methods of removing calcium from crude oil by removing calcium from calcium naphthenate using an acid compound such as sulfuric acid, carboxylic acid ester, water-soluble hydroxyl acid, or maleic acid.
U.S. Pat. No. 5,593,573 discloses the use of sulfuric acid or salts thereof as a calcium removal agent. In this case, an excess of precipitation inhibitor has to be used in order to prevent large amounts of calcium sulfate from being produced during the desalting process, which is undesirable.
Also, Korean Patent No. 10-1340718 discloses a method of removing calcium from a hydrocarbon fraction using maleic acid or derivatives thereof. When this method is applied to crude oil or hydrocarbon fractions containing water, precipitated calcium is known to flow up along the crude oil or hydrocarbon fraction, which is undesirable.
Therefore, it is necessary to develop a method of effectively removing calcium from a hydrocarbon fraction such as crude oil.